Hybrid auto-focus operation which does not perform distance detection focusing if the lens is at a predetermined closest distance side

ABSTRACT

When the present position of a focus lens is on the closest distance side with respect to a predetermined position, the focus lens is driven and controlled using a TV-AF method without using the output result of an external ranging unit, and thereby a malfunction of an AF control due to parallax between an image pickup optical system and an external sensor is prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a focusing technique.

2. Description of the Related Art

There are various automatic focusing (hereinafter also referred to asAF) control methods for image pickup apparatuses such as video cameras.In a so-called TV-AF method, a predetermined high frequency component(contrast component) of an image signal is extracted, and a focusinglens is controlled so that an AF signal corresponding to the sharpnessof the image is largest. In another method, information corresponding tothe distance to the object is obtained by measuring the phase differenceof the object or by triangulation. A combination of these methods(hybrid AF control method) is proposed in Japanese Patent Laid-Open No.2002-258147.

The hybrid AF control method is a combination of the TV-AF method and aninternal measurement method or an external measurement method. In theinternal measurement method, light incident on an image pickup opticalsystem is split and input into a sensor that measures the phasedifference, and the amount of deviation between the focal position andthe in-focus position is measured (the first embodiment of JapanesePatent Laid-Open No. 2002-258147). In the external measurement method, asensor that measures the phase difference is provided separately from animage pickup optical system (the third embodiment of Japanese PatentLaid-Open No. 2002-258147).

In the internal measurement method, the same object image as the objectimage picked up in the image pickup optical system is input into thesensor that measures the phase difference. Therefore, the sensor cansurely capture the object. However, since a light splitting mechanismand the sensor are placed in the lens barrel, the size of the lensbarrel is liable to be large and therefore the size of the image pickupapparatus main body is liable to be large.

In the external measurement method, since the sensor that measures thephase difference is disposed separately from the image pickup opticalsystem, there is a lot of flexibility of layout. Therefore, this methodis advantageous to the size reduction of the apparatus. However, adeviation occurs between the distance to the main object to bephotographed and the distance to the object measured by the sensor thatmeasures the phase difference. Focusing can fail or take a long time. Tosolve this problem, for example, Japanese Patent Laid-Open No. 6-90395proposes a hybrid AF control method in which AF methods are switchedbased on the comparison between the distance measured by a rangingsensor and a predetermined distance.

However, in the above-described external measurement method, since thedistance sensor is disposed independently from the image pickup opticalsystem, a deviation occurs between the optical axis of the image pickupoptical system and the measurement axis of the distance sensor, that isto say, a parallax occurs. FIG. 2 shows the photographing range and themeasuring range of an external sensor that measures the phase differencein the case where a hand is held in front of the image pickup opticalsystem of an image pickup apparatus. In the case where a hand is held infront of the image pickup optical system, as shown in FIG. 2, the objectphotographed through the image pickup optical system (the hand) isdifferent from the object A captured by the external sensor. In thiscase, if the focusing operation is started based on the measurementresult of the external sensor, a malfunction of the hybrid AF control isinduced. For example, focusing on the object of the image pickup opticalsystem fails or takes a long time.

SUMMARY OF THE INVENTION

An aspect of the present invention is directed to preventing amalfunction of an AF control due to parallax between an image pickupoptical system and an external sensor.

According to an aspect of the present invention, there is provided afocusing apparatus including a first detecting unit configured to outputan electric signal from an optical image formed through an image pickupoptical system including a focus lens and detect a focus signal showingthe sharpness of the optical image from the output electric signal, asecond detecting unit configured to detect the in-focus position with anoptical system provided separately from the image pickup optical system,and a control unit configured to drive and control the focus lens basedon the detection result from the first and second detecting units. Thecontrol unit drives and controls the focus lens using the firstdetecting unit without using the second detecting unit when the presentposition of the focus lens is on the closest distance side with respectto a predetermined position.

According to another aspect of the present invention, there is provideda method for controlling a focusing apparatus which includes a firstdetecting unit configured to output an electric signal from an opticalimage formed through an image pickup optical system including a focuslens and detect a focus signal showing the sharpness of the opticalimage from the output electric signal, a second detecting unitconfigured to detect the in-focus position with an optical systemprovided separately from the image pickup optical system, and a controlunit configured to drive and control the focus lens based on thedetection result from the first and second detecting units. The methodincludes the step of driving and controlling the focus lens using thefirst detecting unit without using the second detecting unit when thepresent position of the focus lens is on the closest distance side withrespect to a predetermined position.

Further features and aspects of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example structure of an image pickup apparatus accordingto an embodiment.

FIG. 2 shows the parallax between the optical axis of an image pickupoptical system and the measurement axis of a distance sensor.

FIG. 3 shows an example structure of a phase difference passive distancesensor.

FIG. 4 shows examples of object image signals of the phase differencepassive distance sensor.

FIG. 5 is a flowchart showing an example hybrid AF control process.

FIG. 6 shows the principle of automatic focusing in a TV-AF method.

FIG. 7 is a flowchart showing an example TV-AF control process.

FIG. 8 shows cam locus data.

DESCRIPTION OF THE EMBODIMENTS

Various embodiments, features and aspects of the present invention willnow herein be described with reference to attached drawings.

It is noted that the scope of the present invention is not intended tobe limited by each embodiment described below.

FIG. 1 shows an example structure of an image pickup apparatus havingcharacteristics of the present invention. Reference numeral 101 denotesa first fixed lens unit. Reference numeral 102 denotes a zoom lens unitthat performs zooming (hereinafter referred to as zoom lens). Referencenumeral 103 denotes a stop. Reference numeral 104 denotes a second fixedlens unit. Reference numeral 105 denotes a lens unit that has both afocusing function and a compensation function to compensate for movementof the focal plane due to zooming (hereinafter referred to as focuslens). The zoom lens 102 and the focus lens 105 can be moved in theoptical axis direction (the horizontal direction in the figure) with azoom driving source 110 and a focusing driving source 111, respectively.

In such an inner focus type lens system, even if the object distance isequal, the position of the focus lens 105 for focusing on an imagepickup plane 106 varies depending on the focal length. The reason isthat the focus lens 105 has both a function as a compensator lens and afocusing function.

When the focal length is changed, that is to say, when the zoom lens 102is driven, the position of the focus lens 105 for focusing at a givenobject distance is expressed by curves shown in FIG. 8. In FIG. 8, thelowermost curve corresponds to the position for focusing on an object atinfinity. The uppermost curve corresponds to the position for focusingon an object closest to the image pickup plane.

When an image of an object at a given distance is picked up, zooming canbe performed in an in-focus state by driving the focus lens 105according to the corresponding curved locus shown in FIG. 8 (hereinafteralso referred to as cam locus). In an image pickup apparatus having aninner focus type lens system, the cam locus information shown in FIG. 8is stored, for example, in a below-described microcomputer 114 in someform (loci themselves or functions of lens position). The necessary camlocus is selectable, for example, by index number. Based on the locusinformation, the focus lens 105 is driven relative to the drive of thezoom lens 102.

The incident light from the object, passing through the lens units 101to 105, forms an image on an image pickup element 106. The image pickupelement 106 is a photoelectric conversion element such as a CCD sensoror a CMOS sensor, and converts an object image into an electric signal.The electric signal is read out and amplified by a CDS/AGS circuit 107,and is input into a camera signal processing circuit 108. The camerasignal processing circuit 108 performs a predetermined image signalprocessing, and converts the input signal into a signal for a recordingdevice 109 and a monitoring device 115. The recording device 109 recordsthe object image on a recording medium (for example, a magnetic tape, anoptical disk, or a semiconductor memory). The monitoring device 115displays the object image on an electric view finder or a liquid crystalpanel.

The output from the CDS/AGC circuit 107 is also input into an AF gate112. From the image signals of the whole screen, signals of a screenrange used for focus control are selected. Any screen range can be set,and a plurality of ranges can be set. The output from the AF gate 112 isinput into an AF signal processing circuit 113, and is extracted as anAF signal such as a high-frequency component or a luminance differencecomponent (the difference between the maximum and minimum values of theluminance level of the image signal) used for detecting the in-focuspoint. Normally, when an object is photographed, the extracted AF signalis as shown in FIG. 6. The point at which the AF signal is largest isthe in-focus position.

The camera/AF microcomputer 114 is a microcomputer that controls thewhole image pickup apparatus. The output from the above-described AFsignal processing circuit 113 and the output from a below-describedexternal ranging unit 126 are input into the camera/AF microcomputer 114and are used for hybrid AF control calculation. According to thecalculation result, the camera/AF microcomputer 114 controls theabove-described focusing driving source 111 and performs focus control.

To the camera/AF microcomputer 114 are connected a zoom lens positiondetecting sensor 120 that detects the zoom lens position and a focuslens position detecting sensor 121 that detects the focus lens position.This makes it possible to know where the zoom lens 102 and the focuslens 105 are in their respective movable strokes. For example, in thecase where the focus lens 105 is driven with a voice coil motor (VCM),an MR sensor is used as a focus lens position detecting sensor, and thevoltage value output from the MR sensor when the focus lens 105 moves ismonitored. For example, 2.7 V at infinity to 0 V at the closestdistance. From this, the lens position can be known. Alternatively, ifthe focus lens 105 is driven with a stepping motor, the focus lensposition can be known by counting the number of pulses when the focuslens is driven. Similarly, the zoom lens position can be known bymonitoring the output from the zoom lens position detecting sensor. Thepresent invention is not limited to these sensors. Any sensor can beused as long as it can detect the lens position. Next, the externalranging unit 126 will be described.

The external ranging unit 126 is a sensor that measures and outputsinformation corresponding to the distance to the object by the externalmeasurement method. A plurality of ranging methods are used. FIGS. 3 and4 show the principle of ranging by one of them, a phase differencepassive method. In principle, this external ranging unit 126 candirectly measure the in-focus position. Therefore, the focus lens 105can be moved to the in-focus position at high speed.

In FIG. 3, reference numeral 201 denotes an object, reference numeral202 denotes an imaging lens in a first light path, reference numeral 203denotes a photo detector array in the first light path, referencenumeral 204 denotes an imaging lens in a second light path, andreference numeral 205 denotes a photo detector array in the second lightpath. The photo detector arrays in the first and second light paths aredisposed away from each other by a base length B. The object lighttraveling along the first light path forms an image on the photodetector array 203 due to the first imaging lens 202. The object lighttraveling along the second light path forms an image on the photodetector array 205 due to the second imaging lens 204.

FIG. 4 shows examples of signals of the two object images formed in thefirst and second light paths read out from the photo detector arrays 203and 205. Since the two photo detector arrays are apart from each otherby the base length B, as can be seen from FIG. 3, the object imagesignals deviate by a number X of pixels. A calculating unit calculatesthe correlation between the two signals, shifting the pixel, and obtainsthe amount of pixel shift at which the correlation is largest, therebycalculating X. From X, the base length B, and the focal length f of theimaging lenses 202 and 204, the distance L to the object is obtained bytriangulation using the following formula:L=B·f/X

In addition to such a passive ranging method, there are active methods,for example, a method in which the propagation velocity is measuredusing an ultrasonic sensor, and a triangulation method using an infraredprojector, which is commonly used in compact cameras. This embodiment isnot limited to these ranging methods and is a method in which thein-focus position is detected with an optical system provided at aposition different from the position of the photographing opticalsystem. Next, an example operation of the hybrid AF using the externalranging unit 126 will be described with reference to the flowchart ofFIG. 5.

First, the focusing control is started in step S501. In step S502, aTV-AF control is performed. The TV-AF control will hereinafter bedescribed.

In step S503, the cam locus number corresponding to the present focuslens position is selected. This cam locus number 0, 1, 2 . . . N is anindex number assigned to the relationship between the zoom lens positionand the focus lens position for focusing in each object distance. Thecurves shown in FIG. 8, which constitute cam locus information stored inthe camera/AF microcomputer 114, are numbered in ascending order frombottom (infinite object distance).

In step S503, the index number corresponding to the cam locus on whichthe zoom lens position and the focus lens position intersect isselected. The zoom lens position and the focus lens position can bemonitored by the outputs from the zoom lens position detecting sensor120 and the focus lens position detecting sensor 121.

In step S504, the cam locus number selected in step S503 is comparedwith a predetermined cam locus number. The object distance correspondingto this predetermined cam locus number, where the overlap between thelight flux of the external ranging unit and the light flux of thephotographing optical system is small, leads to misdetection. Such anobject distance is, for example, 30 cm. When the object distance issmaller than 30 cm, even if the external ranging unit 126 obtainsinformation on the object distance, the focus lens is not moved based onthe information, thereby a malfunction of the AF control beingprevented.

If the selected cam locus number is larger than the predetermined camlocus number, the flow returns to step S502, and the TV-AF control iscontinued. In this case, the cam locus number selected in step S503corresponds to a cam locus in the range of TV-AF only shown in FIG. 8.The object distance of the object image detected through thephotographing optical system is small, and the focus lens position is onthe closest distance side. The present focus lens position is on theclosest distance side with respect to the predetermined position. Insuch a state, it is highly possible that the object distance obtained inthe external ranging unit 126 is completely different from the objectdistance of the object image detected through the photographing opticalsystem. Therefore, even if the external ranging unit 126 obtainsinformation on the object distance, the focus lens is not moved based onthe information, thereby a malfunction of the AF control beingprevented.

If the selected cam locus number is smaller than the predetermined camlocus number, it is highly possible that the object distance in theexternal ranging unit 126 corresponds to the object distance of theobject image detected through the photographing optical system. In thiscase, the present focus lens position is on the infinity side withrespect to the predetermined position. In this case, the flow proceedsto step S505, and information corresponding to the object distance iscalculated from the information obtained by the external ranging unit126, and then the flow proceeds to step S506.

In step S506, from information corresponding to the object distancedetected by the external ranging unit 126, the focus lens position forfocusing on the object distance is calculated, and then the flowproceeds to step S507. This is a process for calculating the cam locusof the focus lens position for focusing on the object distance accordingto the detection result in the external ranging unit 126.

In step S507, the focus lens position for focusing on the objectdistance according to the detection result in the external ranging unit126 is compared with the present focus lens position. This is fordetermining whether or not it is appropriate to move the focus lensbased on the detection result of the external ranging unit 126.

If the difference between the lens position calculated from the objectdistance detected by the external ranging unit 126 and the present focuslens position is small, the focal position is not significantlydeviated. Therefore, the flow returns to step S502, and the TV-AFcontrol is continued. If the difference is large, it is determined thatthe focal position is significantly deviated, and the flow proceeds tostep S508. In order to focus on the object distance corresponding to thedetection result in the external ranging unit 126, the focus lens 105 ismoved, and the flow proceeds to step S509.

In step S509, it is determined whether or not the focus lens 105 hasreached the object distance corresponding to the detection result of theexternal ranging unit 126. If the focus lens 105 has not reached thedetected object distance, the flow returns to step S508, and themovement of the focus lens 105 is continued. If the focus lens 105 hasreached the object distance corresponding to the detection result of theexternal ranging unit 126, it is determined that the focus lens 105 hasbeen moved to the vicinity of the in-focus position, and the flowproceeds to step S502. The focus lens 105 is then driven to a moreprecise in-focus position by the TV-AF control. Next, the operation ofthe TV-AF method performed in step S502 will be described with referenceto the flowchart of FIG. 7.

The AF process is started (step S1001). First, the focus lens 105 isminutely driven (step S1002).

Next, it is determined whether or not an in-focus state is achieved bythe minute drive (step S1003). If not, it is determined whether or notthe in-focus direction can be determined by the minute drive (stepS1004). If not, the flow returns to step S1002. If the in-focusdirection can be determined, the focus lens 105 is moved at high speedso that the AF evaluation value increases, by the hill-climbing drive instep S1005.

Next, it is determined whether or not the AF evaluation value is pastthe peak by the hill-climbing drive (step S1006). If not, the flowreturns to step S1005, and the hill-climbing drive is continued. If theAF evaluation value is past the peak, the focus lens 105 is driven inthe reverse direction to return to the peak (step S1007).

It is determined whether or not the AF evaluation value is at the peak(step S1008). If not, the flow returns to step S1007, and the operationfor returning the AF evaluation value to the peak is continued. If theAF evaluation value is at the peak, the flow returns to step S1002, andthe in-focus position of the next moving image is searched by minutelydriving the focus lens 105.

If it is determined that an in-focus state is achieved in step S1003,the focus lens 105 is stopped (step S1009), the AF evaluation value inthe in-focus state is stored (step S1010), and the flow enters the partof restart determination process. The AF evaluation value obtained instep S1011 is compared with the previous AF evaluation value stored instep S1010. If there is a difference at a predetermined level or higher,it is determined that a restart is necessary (step S1012).

If it is determined that a restart is necessary, the flow returns tostep S1002, and the minute drive is restarted. If it is not determinedthat a restart is necessary, the focus lens 105 is kept stopped (stepS1013). The flow returns to step S1011, and the restart determinationprocess is continued.

As described above, the TV-AF method drives the focus lens 105,repeating the restart determination, the minute drive, the hill-climbingdrive, the minute drive, and the restart determination, therebycontrolling the AF evaluation value so that the AF evaluation value isalways largest.

As described above, when the present focus lens position is on theclosest distance side, the TV-AF control is performed without using thedetection result of the external ranging unit 126. The present positionof the focus lens is determined from the plurality of cam loci stored inthe camera/AF microcomputer 114. This makes it possible to prevent amalfunction due to parallax in a hybrid AF control of a TV-AF methodthrough an inner focus photographing optical system and an externalmeasurement method. This is effective in the case where the object imagethat the image pickup optical system captures is different from theobject image that the external sensor captures, for example, in the caseof photographing a hand held in front of the image pickup opticalsystem. It is possible to surely focus on the object in thephotographing field angle.

In the above description, the present focus lens position is calculatedbased on the cam locus information. However, the present invention isnot limited to this. The present focus lens position may be calculated,for example, from the number of driving pulses of a stepping motor. Inthis case, it may be determined whether to use the ranging result of theexternal ranging unit 126, by comparing the number of driving pulsescorresponding to the predetermined object distance (30 cm in theabove-described example) with the present number of pulses.

Alternatively, in step S504, it may be determined whether or not thepresent position of the focus lens determined from the stored pluralityof cam loci is smaller than the limit value of the external ranging unit126. For example, when the limit value above which the external rangingunit 126 can measure the amount of deviation between the focal positionand the in-focus position is 20 cm, the object distance obtained fromthe cam locus information may be compared with 20 cm as a threshold.When the object distance is 20 cm or less, since the external rangingunit 126 cannot measure, the output result of the external ranging unit126 is not used.

Other Exemplary Embodiments

The processing described in the above embodiments may be realized byproviding a storage medium, storing program codes of software realizingthe above-described functions, to a computer system or apparatus. Byreading the program codes stored in the storage medium with a computer(or a CPU or MPU) of the system or apparatus and executing them, thefunctions of the above-described embodiments can be realized. In thiscase, the program codes read from the storage medium realize thefunctions according to the embodiments, and the storage medium storingthe program codes constitutes the invention. The storage medium, such asa floppy disk, a hard disk, an optical disk, a magneto-optical disk andthe like can be used for providing the program codes. Also, CD-ROM,CD-R, a magnetic tape, a non-volatile memory card, ROM, and the like canbe used.

Furthermore, the functions according to the above embodiments arerealized not only by executing the program codes read by the computer.The present invention also includes a case where an OS (operatingsystem) or the like working on the computer performs part or the entireprocesses in accordance with designations of the program codes andrealizes the functions according to the above embodiments.

Furthermore, the program codes read from the storage medium may bewritten in a function expansion card which is inserted into the computeror in a memory provided in a function expansion unit which is connectedto the computer. Thereafter, a CPU or the like contained in the functionexpansion card or unit may perform part or the entire processes inaccordance with designations of the program codes and may realize thefunctions of the above embodiments.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No.2006-232350 filed Aug. 29, 2006, which is hereby incorporated byreference herein in its entirety.

1. A focusing apparatus comprising: a first detecting unit configured tooutput an electric signal from an optical image formed through an imagepickup optical system including a focus lens and a zoom lens and detecta focus signal showing a sharpness of the optical image from the outputelectric signal; a second detecting unit configured to detect anin-focus position with an optical system provided separately from theimage pickup optical system; a memory recording information indicatingrelation of a focus lens position and the zoom lens positioncorresponding to object distance of an object; and a control unitconfigured to drive and control the focus lens, wherein, while drivingand controlling the focus lens to bring the object into focus inaccordance with a change of a focal length and the object distance, thecontrol unit drives and controls the focus lens using the output fromthe first detecting unit and an output from the second detecting unitwhen the positions of the focus lens and the zoom lens are in a firstrelation, and the control unit drives and controls the focus lens usingthe output from the first detecting unit without using the output fromthe second detecting unit when the positions of the focus lens and thezoom lens are in a second relation that a focus of the image pickupoptical system is on a closer distance side with respect to apredetermined position compared to the first relation, and wherein thecontrol unit determines the in-focus position of the focus lens based onthe outputs from the first detecting unit and the second detecting unitwhen a present position of the focus lens is on an infinity side withrespect to the predetermined position.
 2. The focusing apparatusaccording to claim 1, wherein the control unit has information showing arelationship between the zoom lens position and the focus lens positionfor supporting a plurality of object distances and detects the presentposition of the focus lens based on the information.
 3. The focusingapparatus according to claim 1, wherein the first detecting unit detectsthe focus signal from a high-frequency component of the electric signal.4. The focusing apparatus according to claim 1, wherein the seconddetecting unit detects the in-focus position based on informationcorresponding to the object distance.
 5. The focusing apparatusaccording to claim 1, wherein a light flux of the optical system of thesecond detecting unit and a light flux of a photographing lens do notoverlap at the predetermined position.
 6. The focusing apparatusaccording to claim 1, wherein the second detecting unit cannot detect atthe predetermined position.
 7. An image pickup apparatus comprising: afocusing apparatus including, a first detecting unit configured tooutput an electric signal from an optical image formed through an imagepickup optical system including a focus lens and a zoom lens and detecta focus signal showing a sharpness of the optical image from the outputelectric signal; a second detecting unit configured to detect anin-focus position with an optical system provided separately from theimage pickup optical system; a memory recording information indicatingrelation of a focus lens position and the zoom lens positioncorresponding to object distance of an object; and a control unitconfigured to drive and control the focus lens, wherein, while drivingand controlling the focus lens to bring the object into focus inaccordance with a change of a focal length and the object distance, thecontrol unit drives and controls the focus lens using the output fromthe first detecting unit and an output from the second detecting unitwhen the positions of the focus lens and the zoom lens are in a firstrelation, and the control unit drives and controls the focus lens usingthe output from the first detecting unit without using the output fromthe second detecting unit when the positions of the focus lens and thezoom lens are in a second relation that a focus of the image pickupoptical system is on a closer distance side with respect to apredetermined position compared to the first relation; and an imagepickup unit configured to output an electric signal used in the firstdetecting unit and output an electric signal used for image recording,wherein the control unit determines the in-focus position of the focuslens based on the outputs from the first detecting unit and the seconddetecting unit when a present position of the focus lens is on aninfinity side with respect to the predetermined position.
 8. A methodfor controlling a focusing apparatus which includes, a first detectingunit configured to output an electric signal from an optical imageformed through an image pickup optical system including a focus lens anda zoom lens and detect a focus signal showing a sharpness of the opticalimage from the output electric signal, a second detecting unitconfigured to detect an in-focus position with an optical systemprovided separately from the image pickup optical system, a memoryrecording information indicating relation of a focus lens position and azoom lens position corresponding to object distance of an object, and acontrol unit configured to drive and control the focus lens, the methodcomprising: driving and controlling the focus lens using the output fromthe first detecting unit and an output from the second detecting unitwhen the positions of the focus lens and the zoom lens are in a firstrelation, and driving and controlling the focus lens using the outputfrom the first detecting unit without using the output from the seconddetecting unit when the positions of the focus lens and the zoom lensare in a second relation that a focus of the image pickup optical systemis on a closer distance side with respect to a predetermined positioncompared to the first relation, while driving and controlling the focuslens to bring the object into focus in accordance with a change of afocal length and the object distance, wherein the control unitdetermines the in-focus position of the focus lens based on the outputsfrom the first detecting unit and the second detecting unit when apresent position of the focus lens is on an infinity side with respectto the predetermined position.